Duncansby is an early-stage development with a Crown Estate lease. Islay is construction-ready and was awarded €20.7m of NER300 funding by the European Commission.

"With consents, grid connection and grants secured, this project is the most advanced commercial scale project in the UK after (Atlantis’s) MeyGen, and is expected to achieve financial close in 2016," said Atlantis.

SPR will have a representative on the TPSL board, "ensuring that the enlarged portfolio can benefit from its experience in renewable energy development and operations, and demonstrating commitment to the future of tidal power in the UK”.

Atlantis chief executive Tim Cornelius said: “The UK is now synonymous with tidal power in the same way tech is with Silicon Valley. By 2022, we aim to have at least 640MW of installed capacity in the UK through development of just our existing portfolio and in the process we want to help build a UK-based supply chain based on world class manufacturing.”

SPR chief executive Keith Anderson said: "This agreement will drive momentum in the sector. With our hard work to design and seek consent for the Islay project, it is now ready to go in to construction, heralding an exciting new chapter in the progression of tidal power.”

“This long awaited deal shows that key ocean energy players are moving ahead on tidal and paves the way for ambitious developments in Scotland.

Trade body Ocean Energy Europe chief executive Remi Gruet added: "In a post-COP21 environment, ocean energy will be needed to deliver clean and predictable electricity, balance the grid and develop a European industry creating local jobs. This is a major step in the right direction."